This invention relates to materials used for the electrical contacts of high-power vacuum circuit breakers and which must be as free as possible from welding tendencies causing the contacts to weld together when subjected to arcing caused by opening and closing of the contacts.
Such contact materials may be an alloy of a base metal having a melting point above 1000.degree. C. and below 1800.degree. C., such as copper, nickel, iron, cobalt or titanium, and an alloying metal such as bismuth, tellurium or lead. These alloying metals do not form solid solutions with these base metals, either at all or at most to a very small degree. Therefore, during solidification of the alloy from its molten phase, these alloying metals form precipitations at the grain boundaries of the base metals. These precipitations inhibit the welding tendency when the alloy is used in the form of electrical contacts.
If such an alloy has too large a grain size, the weld inhibiting precipitations may be so widely dispersed as to appreciably reduce their desired effect. Such an alloy, when solidified very rapidly from its liquid phase, such as by casting it in a chilled mold, may be produced with a fine grain size. However, because the alloy inevitably contains some gases dissolved in it while molten, such rapid solidification does not permit adequate removal of these gases, the gases remaining in the solid alloy either as dissolved or bound gases, the resulting gas content exceeding that considered to be permissible when the alloy is used in the form of electrical contacts.
The object of the present invention is to produce an alloy of the kind described having both a fine grain size and a low gas content.